$ D = \left[\begin{array}{rrr}2 & 2 & 0 \\ 1 & 2 & 2 \\ 2 & 1 & 0\end{array}\right]$ What is $ D^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}-\frac{1}{2} & 0 & 1 \\ 1 & 0 & -1 \\ -\frac{3}{4} & \frac{1}{2} & \frac{1}{2}\end{array}\right]$